89. Rhizobium bacteria living in the roots of bean plants or other legumes produce fixed nitrogen, which is one of the essential plant nutrients and which for non-legume crops, such as wheat, normally must be supplied by applications of nitrogen-based fertilizer. So if biotechnology succeeds in producing wheat strains whose roots will play host to Rhizobium bacteria, the need for artificial fertilizers will be reduced. The argument above makes which one of the following assumptions? (A) Biotechnology should be directed toward producing plants that do not require artificial fertilize. (B) Fixed nitrogen is currently the only soil nutrient that must be supplied by artificial fertilizer for growing wheat crops. (C) There are no naturally occurring strains of wheat or other grasses that have Rhizobium bacteria living in their roots. (D) Legumes are currently the only corps that produce their own supply of fixed nitrogen. (E) Rhizobium bacteria living in the roots of wheat would produce fixed nitrogen.
原文中的限制条件是bacteria living in the roots of bean plants or other legumes 但是WHEAT又不是属于其中的哪一种，所以当然是要做出一定的假设咯 至于C的naturally occurring strains of wheat 是否有这样的假设和原文好象没有什么关系嘛
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发表于 2003-11-23 23:01:00
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